This invention relates to a process for producing spherical glass particles.
Glass spheres of relatively small particle size have found use in a wide range of applications such as in electronics and injection molding of plastics.
U.S. Pat. No. 4,435,342 relates to a process in which fine particles are produced by fine molten stream onto a rotating surface which discharges molten droplets against another surface. The particles striking the latter surface are subdivided and collected as ultrafine particles.
U.S. Pat. No. 4,069,045 describes a process wherein a jet of molten metal is impinged against a rotating flat disc. Relatively thin, brittle, easily shattered, and essentially dendrite-free metal flakes are obtained. These flakes are also described in U.S. Pat. No. 4,063,942.
U.S. Pat. No. 4,221,587 relates to a method of making powder by impinging a jet of molten alloy at an acute angle against the inner surface of a rotating cylindrical chill body. As set forth in column 5, the impinging molten material breaks into a stream of discrete droplets which bounce off the surface and move in the direction of the chill surface. Upon impact with the chill surface, the droplets are solidified at a rapid rate. As set forth in column 6, "the glassy metal powder particles . . . have relatively sharp notched edges which enable the particles to interlock during compaction." As set forth in the first example, the particle size of the powder is such that 90% of the particles have a particle size range between about 25 and 300 microns. In the second example, the particle size of the powder ranges between 100 and 1000 microns.
Herbert Herman and Hareesh Bhat, in an article entitled "Metastable Phases Produced by Plasma Spraying" appearing in the proceedings of a symposium sponsored by the TMS-AIME alloy Phases Committee at the Fall meeting of the Metallurgical Society of AIME, Pittsburg, Pa, Oct. 5-9, 1980 describes the high velocity deposition of plasma-melting particles on a substrate. On page 118, the article indicates that good physical and thermal contact should exist between the solidifying liquid and substrate. Liquid spreading occurs away from the impact point. As illustrated in the drawings, the particles have a flat surface adjacent the substrate with a central raised core region and a circular rim area.
U.S. Pat. Nos. 4,076,640, 4,191,556, 4,376,740, 4,490,601, 3,829,538, 4,252,599, 4,474,604, 4,435,342, 3,742, 585, 4,332,617, 4,386,896, 4,264,641, 4,215,084, 4069,045, 4,259,270, 3,907,546, 4,028,095, and 3,909,241, and Canadian Pat. No. 941,690 relate to metal, alloy, or ore powders or particles or melts and are different from the present invention in that the present invention relates to sperhical glass particles.
Spherical glass particles are more difficult to form because of the higher viscosity of glass at its melting point. Therefore there is a tendency to form filaments with glass.
U.S. Pat. No. 3,313,608 describes a method for producing spherical glass beads in which electrical and magnetic fields are used to break up a molten glass stream of about 0.15" in diameter. The beads are of relatively large particle size, with the size range being from about 0.005 to about 0.200 inches in diameter.
One prior art method for forming glass beads of relatively small size is by grinding the glass into small particles followed by injecting the particles into a flame to melt the particles and allow surface tension to form the particles into spheres. One disadvantage of this method is the formation of a large number of glass filaments along with the spheres. In order to be recylced in the operation, the filaments must be re-melted which is a costly operation.
Commercial glass beads have a particle size in the range of 10 micrometers to 53 micrometers with an average diameter of 30 micrometers. Such beads are described in an article entitled "Shear Band Formation in Polycarbonate-Glass Bead Composites," by M. E. J. Decker and D. Heikens, Journal of Materials Science 19 (1984) 3271-3275.
Therefore, a process for producing such spheres would be desirable.